Electrophotographic image forming apparatuses known in the art include laser printers and light-emitting diode (LED) printers. An image forming apparatus includes developer cartridges and a drum unit. The drum unit includes a plurality of photosensitive drums. Each photosensitive drum is rotatable about a drum axis extending in an axial direction. The developer cartridges are removable from the drum unit. When a developer cartridge is attached to the drum unit, a developing roller of the developer cartridge contacts the photosensitive drum of the drum unit.
The drum unit includes a frame for holding a plurality of developer cartridges, and lock levers for locking the developer cartridges held in the frame. Each developer cartridge is attached to a corresponding slot of the frame. Each lock lever is pivotable about a pivot axis extending in the axial direction between a lock position and a release position. When the lock lever is at the lock position, the developer cartridge is locked on the frame. When the lock lever is at the release position, the developer cartridge is removable from the frame.